Thrombus formation in the artificial kidney. Platelet and fibrin(ogen) content of experimental thrombi detected by radioisotope technique.

In vitro studies in a "mini-Kiil" dialyser showed that, in spite of presumably adequate heparinization (2.5 IU/ml plasma), 51Cr-labelled platelets and 125I-labelled fibrin(ogen) deposited on membranes and blood lines, when freshly drawn human blood was dialyzed for 30 min. Platelet retention dominated, with a Cr/I ratio 3 times that of blood. Increasing the heparin concentration led to a reduction both of 51Cr- and 125I-activity, with a slight fall in the Cr/I ratio. Heparin was unable to prevent platelet retention in the dialyser, but the platelet aggregating effect of heparin was shown to be of minor importance compared to its anticoagulant activity and effect on thrombin induced platelet aggregation. Platelet retention by the blood lines exceeded that of the dialyser, in spite of a much smaller surface area. Differences in thrombogenicity between cuprophane and silicone rubber as well as different flow characteristics in the two situations were probably contributory. When heparinized tubing was used, the radioactivity retained was negligible, but membrane radioactivity was unaltered. A considerable reduction in blood radioactivity during dialysis, not accounted for by the deposits above, suggests the additional formation of more loosely attached platelet/fibrin(ogen) masses.